Endocrine factors contributing to the regulation of folliculogenesis (selection of the dominant follicle) during the primate ovarian cycle were examined in two non-human primate models, the rhesus monkey, and the cynomolgus monkey. Circulating patterns of gonadotropins and ovarian steroids (estradiol and progesterone) were monitored by radioimmunoassay before and after follicle cautery, luteectomy and hemiovariectomy during the menstrual cycle in monkeys. In addition to examining follicle growth during the nonfertile menstrual cycle, the resumption of follicle growth was studied during the puerperium. Ovary-conceptus interrelationships, as well as the cessation of follicle growth in pregnancy were studied during the fertile menstrual cycle. Salient findings include: 1) usefulness of the cynomolgus monkey as alternative non-human primate model, 2) asymmetrical function of the two ovaries during the menstrual cycle, 3) a dual stimulatory/inhibitory role for macaque chorionic gonadotropin, 4) evidence that the dominant follicle is selected during the first week of the menstrual cycle, and 5) evidence that FSH secretion is regulated by an ovarian factor(s) other than estradiol or progesterone.